The present invention relates to DNA sequences encoding Vmp-like polypeptides of pathogenic Borrelia, the use of the DNA sequences in recombinant vectors to express polypeptides, the encoded amino acid sequences, application of the DNA and amino acid sequences to the production of polypeptides as antigens for immunoprophylaxis, immunotherapy, and immunodiagnosis. Also disclosed are the use of the nucleic acid sequences as probes or primers for the deletion of organisms causing Lyme disease, relapsing fever, or related disorders, and kits designed to facilitate methods of using the described polypeptides, DNA segments and antibodies.

1. Field of the Invention
The invention relates to the field of molecular biology; in particular, to immunogenic compositions and recombinant VMP-like genes useful for treatment and diagnosis of Lyme disease. Also included are methods for the determination of virulence factors in Lyme disease.
2. Description of Related Art
Lyme disease is a bacterial infection caused by pathogenic spirochetes of the genus Borrelia. The infection can occur in humans, dogs, deer, mice and other animals, and is transmitted by arthropod vectors, most notably ticks of the genus Ixodes. Borrelia burgdorferi, the most common cause of Lyme disease in North America, was first cultured in 1982. B. garinii and B. afzelii are the most common infectious agents of Lyme disease in Europe, and another species, B. japonicum, has been described in Japan. These organisms are closely related and cause similar manifestations with multiple stages: an expanding rash at the site of the tick bite (erythema migrans); fever, lymphadenopathy, fatigue, and malaise; effects of disseminated infection, including carditis, meningoradiculitis, and polyarthritis; and chronic manifestations including arthritis and neurologic disorders. Lyme disease is often difficult to diagnose because of shared manifestations with other disorders, and it can also be refractory to treatment during late stages of the disease. It is most common in areas such as suburban regions of upstate New York and Connecticut, where large populations of deer and white-footed mice serve as the principal mammalian hosts and reservoirs of infection. Approximately 10,000 cases of Lyme disease in humans are reported per year in the United States. and it is also a significant veterinary problem due to a high infection rate of dogs and other domestic animals in endemic regions.
B. burgdorferi, the etiologic agent of Lyme disease, is able to persist for years in patients or animals despite the presence of an active immune response (Steer, 1989; Schutzer, 1992). Antigenic variation has been postulated previously as a mechanism whereby B. burgdorferi evades the immune response in the mammalian host (Schwan et al., 1991; Wilske et al., 1992). Antigenic variation has been defined as changes in the structure or expression of antigenic proteins that occurs during infection at a frequency greater than the usual mutation rate (Borst and Geaves, 1987; Robertson and Meyer, 1992; Seifert and So, 1988).
Relapsing fever is another disease caused by pathogenic Borrelia. It has both epidemic and endemic forms. The epidemic form is caused by B. recurrentis and is transmitted between humans by lice. It was a major source of morbidity and mortality during World War I, but has been rare since then due largely to public health measures. Endemic relapsing fever is an epizootic infection caused by several Borreliae species, including B. hermsii. It occurs sporadically among hunters, spelunkers, and others who come in contact with infected soft-bodied ticks of the genus Ornithidorus. Relapsing fever is characterized by two or more episodes or xe2x80x9crelapsesxe2x80x9d of high bacteremia (up to 108/ml). The first wave of infection is caused by Borreliae expressing a certain Variable Major Protein (VMP) on their surface (e.g. Vmp21). The gene encoding this VMP is located at a promoter site in the expression plasmid, whereas over 24 nonexpressed copies of different VMP genes are present on the so-called silent plasmid. When the host develops antibodies against the expressed VMP, the organisms of that stereotype are destroyed and the patient improves. However, a small proportion of organisms have undergone antigenic switching to a different stereotype. Nonreciprocal recombination occurs between the expression plasmid and the silent plasmid, resulting in the insertion of a different VMP gene in the expression site (e.g., Vmp7). The organisms expressing Vmp7 are not affected by the anti-Vmp21 antibodies, and therefore multiply in the host and cause a second episode of the disease. Up to five of these 3-5 day episodes can occur, separated by 1-2 week intervals.
Such well-demarcated episodes of infection do not occur during Lyme disease, and fewer organisms are present in the blood and in tissues at any stage. However, there are reasons to suspect that similar mechanisms of antigenic variation may occur in B. burgdorferi and other Lyme disease Borreliae. The infection, if untreated, commonly persists for months to years despite the occurrence of host antibody and cellular responses; this observation indicates effective evasion of the immune response. Lyme disease may be disabling (particularly in its chronic form), and thus there is a need for effective therapeutic and prophylactic treatment.
Certain B burgdorferi genes and proteins have been patented, including Outer Surface Protein D (OspD) (U.S. Pat. No. 5,246,844; issued Sep. 21, 1993). OspD has not proven to be a useful protein for diagnosis or immunoprotection. Other proteins, including OspA and OspC, have been considered as vaccine candidates for Lyme disease, including a recombinant OspA vaccine currently in human clinical trials. Other vaccines are in use or undergoing testing in veterinary applications, including vaccination of dogs. However, animal studies indicate that OspA vaccination may not be effective against all strains of Lyme disease Borreliae. OspA is also not useful for immunodiagnosis, due to weak antibody responses to OspA in Lyme disease patients.
Previous studies have generally failed to provide evidence for the occurrence of antigenic variation in Lyme disease Borrelia. Genetic heterogeneity in the genes encoding the membrane lipoproteins OspA, OspB, OspC, and OspD has been well documented among strains of Lyme disease Borreliae (Marconi et al., 1993; Marconi et al., 1994; Livey et al., 1995). In addition, mutations in ospA and ospB have been shown to occur in vitro (Rosa et al., 1992; Sadziene et al., 1992). However, no significant antigenic change (Barthold, 1993) or gross genetic alteration (Persing et al., 1994; Stevenson et al., 1994) has been detected in B. burgdorferi N40 isolates from chronically infected BALB/c and C3H mice, other than the loss of the 38-kilobase (kb) plasmid encoding OspD. Therefore the heterogeneity in Osp proteins observed among B. burgdorferi sensu lato isolates appears to represent evolutionary divergence (xe2x80x9cantigenic driftxe2x80x9d) rather than antigenic variation.
There is a commercial demand for vaccines and diagnostic kits for Lyme disease, both for human and veterinary use. Several companies have active research and development programs in these areas.
Partial and complete DNA sequences have been determined for several recombinant clones containing DNA encoding VMP-like sequences. The identification and characterization of these sequences now allows: (1) identification of the expressed gene(s) in B. burgdorferi; (2) expression of these gene(s) by a recombinant vector in a host organism such as E. coli; (3) immunization of laboratory animals with the resulting polypeptide, and determination of protective activity against B. burgdorferi infection; (4) use of antibodies against the expressed protein to identify the reactive polypeptide(s) in B. burgdorferi cells; (5) use of the expressed protein(s) to detect antibody responses in infected humans and animals; (6) determination of the presence, sequence differences, and expression of the VMP-like DNA sequences in other Lyme disease Borreliae.
The invention is contemplated to be useful in the immunoprophylaxis, diagnosis, or of Lyme disease, relapsing fever, or related diseases in humans or animals. It is expected that recombinant or native proteins expressed by the VMP-like genes (or portions thereof) will be useful for (a) immunoprophylaxis against Lyme disease, relapsing fever, or related disorders in humans and animals; (b) immunotherapy of existing Lyme disease, relapsing fever, or related illnesses, by way of immunization of injection of antibodies directed against VMP-like proteins; and (c) immunodiagnosis of Lyme disease, relapsing fever, or related diseases, including their use in kits in which the VMP-like proteins are the sole antigen or one of multiple antigens. The DNA may be employed in: (a) production of recombinant DNA plasmids or other vectors capable of expressing recombinant polypeptides; and (b) design and implementation of nucleic acid probes or oligonucleotides for detection and/or amplification of VMP-like sequences. The latter is expected to have application in the diagnosis of infection with Borrelial organisms.
Similar sequences in B. burgdorferi and other Lyme disease Borreliae have not been reported previously, as determined by BLAST searches of current nucleotide and amino acid databases including Genbank, the EMBL DNA database, and the Swiss Protein database. Although there is some similarity between the B. burgdorferi deduced amino acid sequences with previously published B. hermsii VMP deduced amino acid sequences, the degree of identity and similarity is only xcx9c30% and xcx9c50%, respectively. Outer surface protein C (OspC) of Lyme disease organisms has been reported to have sequence similarities to VMPs, but the highest similarity is to a different subgroup of VMPs than the sequences reported here (Carter et al., 1994). The VMP-like sequences such as those contained in pJRZ53-31 have a low degree of homology with OspC from some Lyme disease organisms (e.g. B. burgdorferi 2591), as indicated by a BLASTP homology score of 60 and a probability of 0.0013. Thus, the B. burgdorferi VMP-like DNA sequences are unique, although they have an apparent evolutionary relationship with other Borrelia genes.
Another aspect of the invention is the method for identification of possible virulence factors. This approach entails subtractive hybridization of target DNA from high infectivity organisms with driver DNA from low-infectivity strains or clones. This procedure greatly enriches for sequences which differ between the high- and low-infectivity strains and thus may encode proteins important in virulence. Of particular utility is the use of closely related isogenic clones that differ in their infectivity; in this case, the DNA differences should be restricted more stringently to those related to infectivity.
Open reading frames in a B. burgdorferi plasmid that encode hypothetical proteins resembling the VMP proteins of relapsing fever organisms have now been identified. The inventors have found that the presence of the plasmid containing these VMP-like sequences in B. burgdorferi clones correlates strongly with infectivity. Thus it is likely that the proteins encoded by the VMP-like sequences are important in immunoprotection and pathogenesis. Proteins encoded by the VMP-like sequences of B. burgdorferi may provide protection when used either alone or in combination with other antigens. They may also be useful for immunodiagnosis.
The invention is considered to include DNA segments corresponding to 20, 30, and 40 base pairs of the VMP-like sequences; DNA segments inclusive of the entire open leading frames of the VMP-like sequences; amino acid sequences corresponding to both conserved and variable regions of the VMP-like sequences; recombinant vectors encoding an antigenic protein corresponding to the above amino acid sequences; recombinant cells where extrachromosomal DNA expresses a polypeptide encoded by the DNA encoding Borrelia VMP-like sequences; a recombinant B. burgdorferi or E. coli cell containing the DNA encoding VMP-like sequences; methods of preparing transformed bacterial host cells using the DNA encoding the VMP-like polypeptides; methods using the plasmid or vector to transform the bacterial host cell to express B. burgdorferi polypeptides encoded by the DNA sequences; methods for immunization of humans or animals with the native B. burgdorferi polypeptide or polypeptides expressed by recombinant cells that include DNA encoding the VMP-like polypeptides; and methods for identifying potential virulence factors using subtractive hybridization between target DNA from high-infectivity cells and driver DNA from low-infectivity cells.
Also included in the invention are primer sets capable of priming amplification of the VMP-like DNA sequences; kits for the detection of B. burgdorferi nucleic acids in a sample, the kits containing a nucleic acid probe specific for the VMP-like sequences, together with a means for detecting a specific hybridization with the probe; kits for detection of antibodies against the VMP-like sequences of B. burgdorferi and kits containing a native or recombinant VMP-like polypeptide, together with means for detecting a specific binding of antibodies to the antigen.
Methods of Treatment
An important aspect of the invention is the recognition that Borrelia VMP-like sequences recombine at the vls site, with the result that antigenic variation is virtually limitless. Multiclonal populations therefore can exist in an infected patient so that immunological defenses are severely tested if not totally overwhelmed. Thus there is now the opportunity to develop more effective combinations of immunogens for protection against Borrelia infections or as preventive inoculations such as in the form of cocktails of multiple antigenic variants based on a base series of combinatorial VMP-like antigens.
VMP-like protein preparations may be administered in several ways, either locally or systematically in pharmaceutically acceptable formulations. Amounts appropriate for administration are determined on an individual basis depending on such factors as age and sex of the subject, as well as physical condition and weight. Such determinations are well within the skill of the practitioner in the medical field.
Other methods of administration may include injection of Borrelia VMP-like DNAs into vaccine recipients (human or animal) driven by an appropriate promoter such as CMV, (so called DNA vaccines). Such preparations could be injected directly into lesions or transplanted into patients for systemic immunization. DNA vaccinations techniques are currently well past the initial development stage and have shown promise as vaccination strategies.
VMP-like Genes
Recombinant proteins and polypeptides encoded by isolated DNA segments and genes are often referred to with the prefix xe2x80x9crxe2x80x9d for recombinant. As such, DNA segments encoding rVMPs, or rVMP-related genes, etc. are contemplated to be particularly useful in connection with this invention. Any recombinant vls combining any of the vlsE expression site loci and/or silent vls cassettes (vls2-vls-16) gene would likewise be very useful with the methods of the invention.
Isolation of the DNA encoding VMP polypeptides allows one to use methods well known to those of skill in the art and as herein described to make changes in the codons for specific amino acids such that the codons are xe2x80x9cpreferred usagexe2x80x9d codons for a given species. Thus for example, preferred codons will vary significantly for bacterial species as compared with mammalian species however, there are preferences even among related species. Shown below is a preferred codon usage table human. Isolation of spirochete DNA encoding VMP will allow substitutions for preferred human codons, although expressed polypeptide product from human DNA is expected to be homologous to bacterial VMP and so would be expected to be structurally and functionally equivalent to VMP isolated from a spirochete. However, substitutions of preferred human codons may improve expression in the human host, thereby improving the efficiency of potential DNA vaccines.
The definition of a xe2x80x9cVMP-like genexe2x80x9d, xe2x80x9cVMP-related genexe2x80x9d as used herein, is a gene that hybridizes, under relatively stringent hybridization conditions (see, e.g., Maniatis et al., 1982), to DNA sequences presently known to include related gene sequences.
To prepare an VMP-like gene segment or cDNA one may follow the teachings disclosed herein and also the teachings of any of patents or scientific documents specifically referenced herein. One may obtain a rVMP- or other related-encoding DNA segments using molecular biological techniques, such as polymerase chain reaction (PCR(trademark)) or screening of a cDNA or genomic library, using primers or probes with sequences based on the above nucleotide sequence. Such fragments may be readily prepared by, for example, directly synthesizing the fragment by chemical means, by application of nucleic acid reproduction technology, such as the PCR(trademark) technology of U.S. Pat. Nos. 4,683,195 and 4,683,202 (herein incorporated by reference). The practice of these techniques is a routine matter for those of skill in the art, as taught in various scientific texts (see e.g., Sambrook et al., 1989), incorporated herein by reference. Certain documents further particularly describe suitable mammalian expression vectors, e.g., U.S. Pat. No. 5,168,050, incorporated herein by reference. The VMP genes and DNA segments that are particularly preferred for use in certain aspects of the present methods are those encoding VMP and VMP-related polypeptides.
It is also contemplated that one may clone other additional genes or cDNAs that encode a VMP or VMP-related peptide, protein or polypeptide. The techniques for cloning DNA molecules, i.e., obtaining a specific coding sequence from a DNA library that is distinct from other portions of DNA, are well known in the art. This can be achieved by, for example, screening an appropriate DNA library which relates to the cloning of a vls gene such as from the variable region of that gene. The screening procedure may be based on the hybridization of oligonucleotide probes, designed from a consideration of portions of the amino acid sequence of known DNA sequences encoding related Borrelia proteins. The operation of such screening protocols is well known to those of skill in the art and are described in detail in the scientific literature, for example, see Sambrook et al., 1989.
Techniques for introducing changes in nucleotide sequences that are designed to alter the functional properties of the encoded proteins or polypeptides are well known in the art, e.g., U.S. Pat. No. 4,518,584, incorporated herein by reference, which techniques are also described in further detail herein. Such modifications include the deletion, insertion or substitution of bases, and thus, changes in the amino acid sequence. Changes may be made to increase the VMP activity of a protein, to increase its biological stability or half-life, to change its glycosylation pattern, and the like. All such modifications to the nucleotide sequences are encompassed by this invention.
VMP-encoding DNA Segments
The present invention, in a general and overall sense, also concerns the isolation and characterization of novel vls gene segments, which encode combinatorial mosaics of expressed and silent regions of the vls gene. A preferred embodiment of the present invention is a purified nucleic acid segment that encodes a protein that has at least a partial amino acid sequence in accordance with SEQ ID NO:2. Another embodiment of the present invention is a purified nucleic acid segment, further defined as including nucleotide sequences in accordance with SEQ ID NO:1 and SEQ ID NO:3.
In a more preferred embodiment the purified nucleic acid segment consists essentially of the nucleotide sequence of SEQ ID NO:1 and SEQ ID NO:3, their complement or the degenerate variants thereof. As used herein, the term xe2x80x9cnucleic acid segmentxe2x80x9d and xe2x80x9cDNA segmentxe2x80x9d are used interchangeably and refer to a DNA molecule which has been isolated free of total genomic DNA of a particular species. Therefore, a xe2x80x9cpurifiedxe2x80x9d DNA or nucleic acid segment as used herein, refers to a DNA segment which contains a VMP coding sequence yet is isolated away from, or purified free from, total genomic DNA, for example, total cDNA or borrelia genomic DNA. Included within the term xe2x80x9cDNA segmentxe2x80x9d, are DNA segments and smaller fragments of such segments, and also recombinant vectors, including, for example, plasmids, cosmids, phage, viruses, and the like.
Similarly, a DNA segment comprising an isolated or purified vls gene refers to a DNA segment including VMP-related coding sequences isolated substantially away from other naturally occurring genes or protein encoding sequences. In this respect, the term xe2x80x9cgenexe2x80x9d is used for simplicity to refer to a functional protein, polypeptide or peptide encoding unit. As will be understood by those in the art, this functional term includes both genomic sequences, cDNA sequences or combinations thereof. xe2x80x9cIsolated substantially away from other coding sequencesxe2x80x9d means that the gene of interest, in this case vls, forms the significant part of the coding region of the DNA segment, and that the DNA segment does not contain large portions of naturally-occurring coding DNA, such as large chromosomal fragments or other functional genes or cDNA coding regions. Of course, this refers to the DNA segment as originally isolated, and does not exclude genes or coding regions later added to the segment by the hand of man, nor are other portions or contiguous sequences of naturally occurring DNA excluded.
In particular embodiments, the invention concerns isolated DNA segments and recombinant vectors incorporating DNA sequences which encode a VMP-like protein that includes within its amino acid sequence an amino acid sequence in accordance with SEQ ID NO:2.
Another preferred embodiment of the present invention is a purified nucleic acid segment that encodes a protein in accordance with SEQ ID NO:2, further defined as a recombinant vector. As used herein the term, xe2x80x9crecombinant vectorxe2x80x9d, refers to a vector that has been modified to contain a nucleic acid segment that encodes an VMP protein, or a fragment thereof. The recombinant vector may be further defined as an expression vector comprising a promoter operatively linked to said VMP-encoding nucleic acid segment.
A further preferred embodiment of the present invention is a host cell, made recombinant with a recombinant vector comprising an vls gene. The recombinant host cell may be a prokaryotic cell. As used herein, the term xe2x80x9cengineeredxe2x80x9d or xe2x80x9crecombinantxe2x80x9d cell is intended to refer to a cell into which a recombinant gene, such as a gene encoding VMP, has been introduced. Therefore, engineered cells are distinguishable from naturally occuring cells which do not contain a recombinantly introduced gene. Engineered cells are thus cells having a gene or genes introduced through the hand of man. Recombinantly introduced genes will either be in the form of a copy of a genomic gene or a cDNA gene, or will include genes positioned adjacent to a promoter not naturally associated with the particular introduced gene.
In certain embodiments, the invention concerns isolated DNA segments and recombinant vectors which encode a protein or peptide that includes within its amino acid sequence an amino acid sequence essentially as set forth in SEQ ID NO:2. Naturally, where the DNA segment or vector encodes a full length VMP-like protein, or is intended for use in expressing the VMP-like protein, the most preferred sequences are those which are essentially as set forth in SEQ ID NO:2. It is recognized that SEQ ID NO:2 represents the full length protein encoded by the vls gene and that contemplated embodiments include up to the full length sequence and functional variants as well.
The term xe2x80x9ca sequence essentially as set forth in SEQ ID NO:2xe2x80x9d means that the sequence substantially corresponds to a portion of SEQ ID NO:2 and has relatively few amino acids which are not identical to, or a biologically functional equivalent of, the amino acids of SEQ ID NO:2. The term xe2x80x9cbiologically functional equivalentxe2x80x9d is well understood in the art and is further defined in detail herein, as a gene having a sequence essentially as set forth in SEQ ID NO:1 and that is associated with a vls gene in the Borrelia family. Accordingly, sequences which have between about 70% and about 80%; or more preferably, between about 85% and about 90%; or even more preferably, between about 90 and 95% and about 99%; of amino acids which are identical or functionally equivalent to the amino acids of SEQ ID NO:2 will be sequences which are xe2x80x9cessentially as set forth in SEQ ID NO:2xe2x80x9d.
In certain other embodiments, the invention concerns isolated DNA segments and recombinant vectors that include within their sequence a nucleic acid sequence essentially as set forth in SEQ ID NO:1 and SEQ ID NO:3. The term xe2x80x9cessentially as set forth in SEQ ID NO:1 and SEQ ID NO3,xe2x80x9d is used in the same sense as described above and means that the nucleic acid sequence substantially corresponds to a portion of SEQ ID NO:1 and SEQ ID NO:3, and has relatively few codons which are not identical, or functionally equivalent, to the codons of SEQ ID NO:1 and SEQ ID NO:3. The term xe2x80x9cfunctionally equivalent codonxe2x80x9d is used herein to refer to codons that encode the same amino acid, such as the six codons for arginine or serine, as set forth in Table 4, and also refers to codons that encode biologically equivalent amino acids.
It will also be understood that amino acid and nucleic acid sequences may include additional residues, such as additional N- or C-terminal amino acids or 5xe2x80x2 or 3xe2x80x2 sequences, and yet still be essentially as set forth in one of the sequences disclosed herein, so long as the sequence meets the criteria set forth above, including the maintenance of biological protein activity where protein expression is concerned. The addition of terminal sequences particularly applies to nucleic acid sequences which may, for example, include various non-coding sequences flanking either of the 5xe2x80x2 or 3xe2x80x2 portions of the coding region or may include various internal sequences, i.e., introns, which are known to occur within genes.
Excepting intronic or flanking regions, and allowing for the degeneracy of the genetic code, sequences which have between about 70% and about 80%; or more preferably, between about 80%, 85% and about 90%; or even more preferably, between about 90%, 95% and about 99%; of nucleotides which are identical to the nucleotides of SEQ ID NO:1 and SEQ ID NO:3 will be sequences which are xe2x80x9cessentially as set forth in SEQ ID NO:1 and SEQ ID NO:3xe2x80x9d. Sequences which are essentially the same as those set forth in SEQ ID NO:1 and SEQ ID NO:3 may also be functionally defined as sequences which are capable of hybridizing to a nucleic acid segment containing the complement of SEQ ID NO:1 and SEQ ID NO:3 under relatively stringent conditions or conditions of high stringency. Suitable relatively stringent hybridization conditions will be well known to those of skill in the art and are clearly set forth herein, for example conditions for use with Southern and Northern blot analysis, and as described in the examples herein set forth.
Naturally, the present invention also encompasses DNA segments which are complementary, or essentially complementary, to the sequence set forth in SEQ ID NO:1 and SEQ ID NO:3. Nucleic acid sequences which are xe2x80x9ccomplementaryxe2x80x9d are those which are capable of base-pairing according to the standard Watson-Crick complementary rules. As used herein the term xe2x80x9ccomplementary sequencesxe2x80x9d means nucleic acid sequences which are substantially complementary, as may be assessed by the same nucleotide comparison set forth above, or as defined as being capable of hybridizing to the nucleic acid segment of SEQ ID NO:1 and SEQ ID NO:3 under relatively stringent conditions, i.e., conditions of high stringency.
The nucleic acid segments of the present invention, regardless of the length of the coding sequence itself, may be combined with other DNA sequences, such as promoters, polyadenylation signals, additional restriction enzyme sites, multiple cloning sites, other coding segments, and the like, such that their overall length may vary considerably. It is therefore contemplated that a nucleic acid fragment of almost any length may be employed, with the total length preferably being limited by the ease of preparation and use in the intended recombinant DNA protocol. For example, nucleic acid fragments may be prepared which include a short stretch complementary to SEQ ID NO:1 and SEQ ID NO:3, such as about 10 to 15 or 20, 30, or 40 or so nucleotides, and which are up to 2000 or so base pairs in length. DNA segments with total lengths of about 8000, 7000, 6000, 5000, 4000, 3000, 2000, 1000, 500, 200, 100 and about 50 base pairs in length are also contemplated to be useful.
A preferred embodiment of the present invention is a nucleic acid segment which comprises at least a 14-nucleotide long stretch which corresponds to, or is complementary to, the nucleic acid sequence of SEQ ID NO:1 and SEQ ID NO:3. In a more preferred embodiment the nucleic acid is further defined as comprising at least a 20 nucleotide long stretch, a 30 nucleotide long stretch, 50 nucleotide long stretch, 100 nucleotide long stretch, or at least an 2000 nucleotide long stretch which corresponds to, or is complementary to, the nucleic acid sequence of SEQ ID NO:1 and SEQ ID NO:3. The nucleic acid segment may be further defined as having the nucleic acid sequence of SEQ ID NO:1 and SEQ ID NO:3.
A related embodiment of the present invention is a nucleic acid segment which comprises at least a 14-nucleotide long stretch which corresponds to, or is complementary to, the nucleic acid sequence of SEQ ID NO:1 and SEQ ID NO:3, further defined as comprising a nucleic acid fragment of up to 10,000 basepairs in length. A more preferred embodiment if a nucleic acid fragment comprising from 14 nucleotides of SEQ ID NO:1 and SEQ ID NO:3 up to 5,000 basepairs in length, 3,000 basepairs in length, 2,000 basepairs in length, 1,000 basepairs in length, 500 basepairs in length, or 100 basepairs in length.
Naturally, it will also be understood that this invention is not limited to the particular nucleic acid and amino acid sequences of SEQ ID NO:1 and SEQ ID NO:3. Recombinant vectors and isolated DNA segments may therefore variously include the VMP-like protein coding regions themselves, coding regions bearing selected alterations or modifications in the basic coding region, or they may encode larger polypeptides which nevertheless include VMP-coding regions or may encode biologically functional equivalent proteins or peptides which have variant amino acids sequences.
The DNA segments of the present invention encompass biologically functional equivalent VMP-like proteins and peptides. Such sequences may arise as a consequence of codon redundancy and functional equivalency which are known to occur naturally within nucleic acid sequences and the proteins thus encoded. Alternatively, functionally equivalent proteins or peptides may be created via the application of recombinant DNA technology, in which changes in the protein structure may be engineered, based on considerations of the properties of the amino acids being exchanged. Changes designed by man may be introduced through the application of site-directed mutagenesis techniques, e.g., to introduce improvements to the antigenicity of the VMP-like protein or to test VMP-like mutants in order to examine activity or determine the presence of VMP-like peptide in various cells and tissues at the molecular level.
A preferred embodiment of the present invention is a purified composition comprising a polypeptide having an amino acid sequence in accordance with SEQ ID NO:2. The term xe2x80x9cpurifiedxe2x80x9d as used herein, is intended to refer to an VMP-related protein composition, wherein the VMP-like protein is purified to any degree relative to its naturally-obtainable state, i.e., in this case, relative to its purity within a eukaryotic cell extract. A preferred cell for the isolation of VMP-like protein is from borrelia organisms; however, VMP-like protein may also be isolated from various patient specimens, specimens from infected animals, recombinant cells, tissues, isolated subpopulations of tissues, and the like, as will be known to those of skill in the art, in light of the present disclosure. A purified VMP-like protein composition therefore also refers to a polypeptide having the amino acid sequence of SEQ ID NO:2, free from the environment in which it may naturally occur.
If desired, one may also prepare fusion proteins and peptides, e.g., where the VMP-like protein coding regions are aligned within the same expression unit with other proteins or peptides having desired functions, such as for purification or immunodetection purposes (e.g., proteins which may be purified by affinity chromatography and enzyme label coding regions, respectively).
Turning to the expression of the vls gene whether from cDNA based or genomic DNA, one may proceed to prepare an expression system for the recombinant preparation of VMP-like protein. The engineering of DNA segment(s) for expression in a prokaryotic or eukaryotic system may be performed by techniques generally known to those of skill in recombinant expression. For example, one may prepare a VMP-GST (glutathione-S-transferase) fusion protein that is a convenient means of bacterial expression. However, it is believed that virtually any expression system may be employed in the expression of VMP-like proteins.
VMP-like proteins may be successfully expressed in eukaryotic expression systems, however, the inventors contemplate that bacterial expression systems may be used for the preparation of VMP for all purposes. The cDNA containing vls gene may be separately expressed in bacterial systems, with the encoded proteins being expressed as fusions with xcex2-galactosidase, avidin, ubiquitin, Schistosoma japonicum glutathione S-transferase, multiple histidines, epitope-tags and the like. It is believed that bacterial expression will ultimately have advantages over eukaryotic expression in terms of ease of use and quantity of materials obtained thereby.
It is proposed that transformation of host cells with DNA segments encoding VMP-like proteins will provide a convenient means for obtaining a VMP-like protein. It is also proposed that cDNA, genomic sequences, and combinations thereof, modified by the addition of a eukaryotic or viral promoter, are suitable for eukaryotic expression, as the host cell will, of course, process the genomic transcripts to yield functional mRNA for translation into protein.
Another embodiment is a method of preparing a protein composition containing growing recombinant host cell comprising a vector that encodes a protein which includes an amino acid sequence in accordance with SEQ ID NO:2, under conditions permitting nucleic acid expression and protein production followed by recovering the protein so produced. The host cell, conditions permitting nucleic acid expression, protein production and recovery, will be known to those of skill in the art, in light of the present disclosure of the vls gene.
Gene Constructs and DNA Segments
As used herein, the terms xe2x80x9cgenexe2x80x9d and xe2x80x9cDNA segmentxe2x80x9d are both used to refer to a DNA molecule that has been isolated free of total genomic DNA of a particular species. Therefore, a gene or DNA segment encoding an VMP-like polypeptide refers to a DNA segment that contains sequences encoding an VMP-like protein, but is isolated away from, or purified free from, total genomic DNA of the species from which the DNA is obtained. Included within the term xe2x80x9cDNA segmentxe2x80x9d, are DNA segments and smaller fragments of such segments, and also recombinant vectors, including, for example, plasmids, cosmids, phage, retroviruses, adenoviruses, and the like.
The term xe2x80x9cgenexe2x80x9d is used for simplicity to refer to a functional protein or peptide encoding unit. As will be understood by those in the art, this functional term includes both genomic sequences and cDNA sequences. xe2x80x9cIsolated substantially away from other coding sequencesxe2x80x9d means that the gene of interest, in this case, a VMP-like protein encoding gene, forms the significant part of the coding region of the DNA segment, and that the DNA segment does not contain large portions of naturally-occurring coding DNA, such as large chromosomal fragments or other functional genes or cDNA coding regions. Of course, this refers to the DNA segment as originally isolated, and does not exclude genes or coding regions, such as sequences encoding leader peptides or targeting sequences, later added to the segment by the hand of man.
Recombinant Vectors Expressing VMP-like Proteins
A particular aspect of this invention provides novel ways in which to utilize VMP-encoding DNA segments and recombinant vectors comprising vls DNA segments. As is well known to those of skill in the art, many such vectors are readily available, one particular detailed example of a suitable vector for expression in mammalian cells is that described in U.S. Pat. No. 5,168,050, incorporated herein by reference. However, there is no requirement that a highly purified vector be used, so long as the coding segment employed encodes a VMP-like protein and does not include any coding or regulatory sequences that would have an adverse effect on cells. Therefore, it will also be understood that useful nucleic acid sequences may include additional residues, such as additional non-coding sequences flanking either of the 5xe2x80x2 or 3xe2x80x2 portions of the coding including, for example, promoter regions, or may include various internal sequences, i.e., introns, which are known to occur within genes.
After identifying an appropriate VMP-encoding gene or DNA molecule, it may be inserted into any one of the many vectors currently known in the art, so that it will direct the expression and production of the VMP-like protein when incorporated into a host cell. In a recombinant expression vector, the coding portion of the DNA segment is positioned under the control of a promoter. The promoter may be in the form of the promoter which is naturally associated with a VMP-encoding gene, as may be obtained by isolating the 5xe2x80x2 non-coding sequences located upstream of the coding segment or exon, for example, using recombinant cloning and/or PCR(trademark) technology, in connection with the compositions disclosed herein.
In certain embodiments, it is contemplated that particular advantages will be gained by positioning the VMP-encoding DNA segment under the control of a recombinant, or heterologous, promoter. As used herein, a recombinant or heterologous promoter is intended to refer to a promoter that is not normally associated with a vls gene in its natural environment. Such promoters may include those normally associated with other borrelia-inhibitory polypeptide genes, and/or promoters isolated from any other bacterial, viral, eukaryotic, or mammalian cell. Naturally, it will be important to employ a promoter that effectively directs the expression of the DNA segment in the particular cell containing the vector comprising a vls gene or gene segment.
The use of recombinant promoters to achieve protein expression is generally known to those of skill in the art of molecular biology, for example, see Sambrook et al., (1989). The promoters employed may be constitutive, or inducible, and can be used under the appropriate conditions to direct high level or regulated expression of the introduced DNA segment. The currently preferred promoters are those such as CMV, RSV LTR, the SV40 promoter alone, and the SV40 promoter in combination with the SV40 enhancer.
Methods of DNA Transfection
Technology for introduction of DNA into cells is well-known to those of skill in the art. Five general methods for delivering a gene into cells have been described: (1) chemical methods (Graham and VanDerEb, 1973); (2) physical methods such as microinjection (Capecchi, 1980), electroporation (Wong and Neumann, 1982; Fromm et al., 1985) and the gene gun (Yang et al., 1990); (3) viral vectors (Clapp, 1993; Danos and Heard, 1992; Eglitis and Anderson, 1988), (4) receptor-mediated mechanisms (Wu et al., 1991; Curiel et al., 1991; Wagner et al., 1992); and (5) direct injection of purified DNA into human or animals.
Liposomes and Nanocapsules
The formation and use of liposomes is generally known to those of skill in the art (see for example, Couvreur et al., 1991 which describes the use of liposomes and nanocapsules in the targeted antibiotic therapy of intracellular bacterial infections and diseases). Recently, liposomes were developed with improved serum stability and circulation half-times (Gabizon and Papahadjopoulos, 1988; Allen and Choun, 1987). The following is a brief description of these DNA delivery modes.
Nanocapsules can generally entrap compounds in a stable and reproducible way (Henry-Michelland et al., 1987). To avoid side effects due to intracellular polymeric overloading, such ultrafine particles (sized around 0.1 mm) should be designed using polymers able to be degraded in vivo. Biodegradable polyalkyl-cyanoacrylate nanoparticles that meet these requirements are contemplated for use in the present invention, and such particles may be are easily made, as described (Couvreur et al., 1984; 1988).
Liposomes are formed from phospholipids that are dispersed in an aqueous medium and spontaneously form multilamellar concentric bilayer vesicles (also termed multilamellar vesicles (MLVs). MLVs generally have diameters ranging from 25 mm to 4 mm. Sonication of MLVs results in the formation of small unilamellar vesicles (SUVs) with diameters in the range of 200 to 500 xc3x85, containing an aqueous solution in the core.
In addition to the teachings of Couvreur et al. (1991), the following information may be utilized in generating liposomal formulations. Phospholipids can form a variety of structures other than liposomes when dispersed in water, depending on the molar ratio of lipid to water. At low ratios the liposome is the preferred structure. The physical characteristics of liposomes depend on pH, ionic strength and the presence of divalent cations. Liposomes can show low permeability to ionic and polar substances, but at elevated temperatures undergo a phase transition which markedly alters their permeability. The phase transition involves a change from a closely packed, ordered structure, known as the gel state, to a loosely packed, less-ordered structure, known as the fluid state. This occurs at a characteristic phase-transition temperature and results in an increase in permeability to ions, sugars and drugs.
Liposomes interact with cells via four different mechanisms: Endocytosis by phagocytic cells of the reticuloendothelial system such as macrophages and neutrophils; adsorption to the cell surface, either by nonspecific weak hydrophobic or electrostatic forces, or by specific interactions with cell-surface components; fusion with the plasma cell membrane by insertion of the lipid bilayer of the liposome into the plasma membrane, with simultaneous release of liposomal contents into the cytoplasm; and by transfer of liposomal lipids to cellular or subcellular membranes, or vice versa, without any association of the liposome contents. It often is difficult to determine which mechanism is operative and more than one may operate at the same time.
Expression of VMP-like Proteins
For the expression of VMP-like proteins, once a suitable (full-length if desired) clone or clones have been obtained, whether they be cDNA based or genomic, one may proceed to prepare an expression system for the recombinant preparation of VMP-like proteins. The engineering of DNA segment(s) for expression in a prokaryotic or eukaryotic system may be performed by techniques generally known to those of skill in recombinant expression. It is believed that virtually any expression system may be employed in the expression of VMP-like proteins.
VMP-like proteins may be successfully expressed in eukaryotic expression systems, however, it is also envisioned that bacterial expression systems may be preferred for the preparation of VMP-like proteins for all purposes. The cDNA for VMP-like proteins may be separately expressed in bacterial systems with the encoded proteins being expressed as fusions with b-galactosidase, ubiquitin, Schistosoma japonicum glutathione S-transferase, green fluorescent protein and the like. It is believed that bacterial expression will ultimately have advantages over eukaryotic expression in terms of ease of use and quantity of materials obtained thereby.
It is proposed that transformation of host cells with DNA segments encoding VMP-like proteins will provide a convenient means for obtaining VMP-like peptides. Both cDNA and genomic sequences are suitable for eukaryotic expression, as the host cell will, of course, process the genomic transcripts to yield functional mRNA for translation into protein.
It is similarly believed that almost any eukaryotic expression system may be utilized for the expression of VMP-like proteins, e.g., baculovirus-based, glutamine synthase-based or dihydrofolate reductase-based systems could be employed. However, in preferred embodiments, it is contemplated that plasmid vectors incorporating an origin of replication and an efficient eukaryotic promoter, as exemplified by the eukaryotic vectors of the pCMV series, such as pCMV5, will be of most use.
For expression in this manner, one would position the coding sequences adjacent to and under the control of the promoter. It is understood in the art that to bring a coding sequence under the control of such a promoter, one positions the 5xe2x80x2 end of the transcription initiation site of the transcriptional reading frame of the protein between about 1 and about 50 nucleotides xe2x80x9cdownstreamxe2x80x9d of (i.e., 3xe2x80x2 of) the chosen promoter.
Where eukaryotic expression is contemplated , one will also typically desire to incorporate into the transcriptional unit which includes VMP-like protein, an appropriate polyadenylation site (e.g., 5xe2x80x2-AATAAA-3xe2x80x2) if one was not contained within the original cloned segment. Typically, the poly A addition site is placed about 30 to 2000 nucleotides xe2x80x9cdownstreamxe2x80x9d of the termination site of the protein at a position prior to transcription termination.
Translational enhancers may also be incorporated as par of the vector DNA. Thus the DNA constructs of the present invention should also preferable contain one or more 5xe2x80x2 non-translated leader sequences which may serve to enhance expression of the gene products from the resulting mRNA transcripts. Such sequences may be derived from the promoter selected to express the gene or can be specifically modified to increase translation of the RNA. Such regions may also be obtained from viral RNAs, from suitable eukaryotic genes, or from a synthetic gene sequence (Griffiths, et al., 1993).
Such xe2x80x9cenhancerxe2x80x9d sequences may be desirable to increase or alter the translational efficiency of the resultant mRNA. The present invention is not limited to constructs where the enhancer is derived from the native 5xe2x80x2-nontranslated promoter sequence, but may also include non-translated leader sequences derived from other non-related promoters such as other enhancer transcriptional activators or genes.
It is contemplated that virtually any of the commonly employed host cells can be used in connection with the expression of VMPs in accordance herewith. Examples include cell lines typically employed for eukaryotic expression such as 239, AtT-20, HepG2, VERO, HeLa, CHO, WI 38, BHK, COS-7, RIN and MDCK cell lines.
It is contemplated that VMP-like protein may be xe2x80x9coverexpressedxe2x80x9d , i.e., expressed in increased levels relative to its natural expression in borrelia cells, or even relative to the expression of other proteins in a recombinant host cell containing VMP-encoding DNA segments. Such overexpression may be assessed by a variety of methods, including radio-labeling and/or protein purification. However, simple and direct methods are preferred, for example, those involving SDS/PAGE and protein staining or Western blotting, followed by quantitative analyses, such as densitometric scanning of the resultant gel or blot. A specific increase in the level of the recombinant protein or peptide in comparison to the level in natural VMP-producing animal cells is indicative of overexpression, as is a relative abundance of the specific protein in relation to the other proteins produced by the host cell and, e.g., visible on a gel.
As used herein, the term xe2x80x9cengineeredxe2x80x9d or xe2x80x9crecombinantxe2x80x9d cell is intended to refer to a cell into which a recombinant gene, such as a gene encoding a VMP peptide has been introduced. Therefore, engineered cells are distinguishable from naturally occurring cells which do not contain a recombinantly introduced gene. Engineered cells are thus cells having a gene or genes introduced through the hand of man. Recombinantly introduced genes will either be in the form of a cDNA gene (i.e., they will not contain introns), a copy of a genomic gene, or will include genes positioned adjacent to a promoter not naturally associated with the particular introduced gene.
It will be understood that recombinant VMPs may differ from naturally produced VMP in certain ways. In particular, the degree of post-translational modifications, such as, for example, lipidation, glycosylation and phosphorylation may be different between the recombinant VMP and the VMP polypeptide purified from a natural source, such as Borrelia.
After identifying an appropriate DNA molecule by any or a combination of means as described above, the DNA may then be inserted into any one of the many vectors currently known in the art and transferred to a prokaryotic or eukaryotic host cell where it will direct the expression and production of the so-called xe2x80x9crecombinantxe2x80x9d version of the protein. The recombinant host cell may be selected from a group consisting of S. mutans, E. coli, S. cerevisae. Bacillus sp., Lactococci sp., Enterococci sp., or Salmonella sp. In certain preferred embodiments, the recombinant host cell will have a recA phenotype.
Where the introduction of a recombinant version of one or more of the foregoing genes is required, it will be important to introduce the gene such that it is under the control of a promoter that effectively directs the expression of the gene in the cell type chosen for engineering. In general, one will desire to employ a promoter that allows constitutive (constant) expression of the gene of interest. The use of these constitutive promoters will ensure a high constant level of expression of the introduced genes. The level of expression from the introduced genes of interest can vary in different clones, probably as a function of the site of insertion of the recombinant gene in the chromosomal DNA. Thus, the level of expression of a particular recombinant gene can be chosen by evaluating different clones derived from each transfection study; once that line is chosen, the constitutive promoter ensures that the desired level of expression is permanently maintained. It may also be possible to use promoters that are subject to regulation, such as those regulated by the presence of lactose analog or by the expression of bacteriophage T7 DNA polymerase.
Recombinant VMP-like Polypeptides
Recombinant versions of a protein or polypeptide are deemed as part of the present invention. Thus one may, using techniques familiar to those skilled in the art, express a recombinant version of the polypeptide in a recombinant cell to obtain the polypeptide from such cells. The techniques are based on cloning of a DNA molecule encoding the polypeptide from a DNA library, that is, on obtaining a specific DNA molecule distinct from other DNAs. One may, for example, clone a cDNA molecule, or clone genomic DNA. Techniques such as these would also be appropriate for the production of the VMP-like polypeptides in accordance with the present invention.
Enhanced Production of VMP-like Proteins
Potential problems with VMP-like proteins isolated from natural sources are low yields and extensive purification processes. An aspect of the present invention is the enhanced production of VMP-like proteins by recombinant methodologies in a bacterial host, employing DNA constructs to transform Gram-positive or Gram-negative bacterial cells. For example, the use of Escherichia coli expression systems is well known to those of skill in the art, as is the use of other bacterial species such as Bacillus subtilis or Streptococcus sanguis.
Further aspects of the invention include high expression vectors incorporating DNA encoding novel vls, combinatorial segments and its variants. It is contemplated that vectors providing enhanced expression of VMP in other systems such as S. mutans will also be obtainable. Where it is desirable, modifications of the physical properties of VMP may be sought to increase its solubility or expression in liquid culture. The vls locus may be placed under control of a high expression promoter or the components of the expression system altered to enhance expression.
In further embodiments, the DNA encoding the VMP-like proteins of the present invention allows for the large scale production and isolation of VMP-like polypeptides. This can be accomplished by directing the expression of the VMP-like polypeptide by cloning the DNA encoding the VMP-like polypeptide into a suitable expression vector. Such an expression vector may then be transformed into a host cell that is able to produce the VMP-like proteins. The VMP-like protein may then be purified, e.g., by means provided for in this disclosure and utilized in a biologically active form. Non-biologically active recombinant VMP-like proteins may also have utility, e.g., as an immunogen to prepare anti-VM antibodies.
Gene Immunization
Adenovirus is particularly suitable for use as a gene transfer vector because of its mid-sized DNA genome, ease of manipulation, high titer, wide target-cell range, and high infectivity. The roughly 36 kB viral genome is bounded by 100-200 base pair (bp) inverted terminal repeats (ITR), in which are contained cis-acting elements necessary for viral DNA replication and packaging. The early (E) and late (L) regions of the genome that contain different transcription units are divided by the onset of viral DNA replication.
The E1 region (E1A and E1B) encodes proteins responsible for the regulation of transcription of the viral genome and a few cellular genes. The expression of the E2 region (E2A and E2B) results in the synthesis of the proteins for viral DNA replication. These proteins are involved in DNA replication, late gene expression, and host cell shut off (Renan, 1990). The products of the late genes (L1, L2, L3, L4 and L5), including the majority of the viral capsid proteins, are expressed only after significant processing of a single primary transcript issued by the major late promoter (MLP). The MLP (located at 16.8 map units) is particularly efficient during the late phase of infection, and all the mRNAs issued from this promoter possess a 5xe2x80x2 tripartite leader (TL) sequence which makes them preferred mRNAs for translation.
In order for adenovirus to be optimized for gene therapy, it is necessary to maximize the carrying capacity so that large segments of DNA can be included. It also is very desirable to reduce the toxicity and immunologic reaction associated with certain adenoviral products.
The large displacement of DNA is possible because the cis elements required for viral DNA replication all are localized in the inverted terminal repeats (ITR) (100-200 bp) at either end of the linear viral genome. Plasmids containing ITR""s can replicate in the presence of a non-defective adenovirus (Hay et al., 1984). Therefore, inclusion of these elements in an adenoviral vector should permit replication.
In addition, the packaging signal for viral encapsidation is localized between 194-385 bp (0.5-1.1 map units) at the left end of the viral genome (Hearing et al., 1987). This signal mimics the protein recognition site in bacteriophage xcex DNA where a specific sequence close to the left end, but outside the cohesive end sequence, mediates the binding to proteins that are required for insertion of the DNA into the head structure. E1 substitution vectors of Ad have demonstrated that a 450 bp (0-1.25 map units) fragment at the left end of the viral genome could direct packaging in 293 cells (Levrero et al., 1991).
It has been shown that certain regions of the adenoviral genome can be incorporated into the genome of mammalian cells and the genes encoded thereby expressed. These cell lines are capable of supporting the replication of an adenoviral vector that is deficient in the adenoviral function encoded by the cell line. There also have been reports of complementation of replication deficient adenoviral vectors by xe2x80x9chelpingxe2x80x9d vectors, e.g., wild-type virus or conditionally defective mutants.
VMP-like Variants
VMP-like related proteins and functional variants are also considered part of the invention. Thus it is expected that truncated and mutated versions of VMP-like protein (SEQ ID NO:2) will afford more convenient and effective forms of VMP for treatment regimens. Thus, any functional version of SEQ ID NO:2, such as truncated species or homologs, and mutated versions of VMP-like protein are considered as part of the invention.
Mutagenized recombinant VMPs may have increased potency and prolonged in vivo half-life, thereby offering more effective long-term treatments. Novel VMPs thus may be obtained by modifications to the vls gene, (such as by site-specific mutagenesis).
Additionally, the 15 silent vls cassettes of B. burgdorferi may be recombined in numerous combinations, providing for example a cocktail of peptide compositions for use as immunogens and to develop vaccines for use in Lyme disease and related conditions.
Pharmaceutical Compositions
Pharmaceutical compositions prepared in accordance with the present invention find use in preventing or ameliorating conditions associated with Borrelia infections, particularly Lyme disease. Such methods generally involve administering a pharmaceutical composition comprising an effective amount of a VMP-like antigen, such as SEQ ID NO:2 or various epitopes thereof. Other exemplary compositions may include an effective amount of either a VMP-like variant or a VMP-like encoding nucleic acid composition. Such compositions may also be used to generate an immune response in an animal in such cases where it may be desirable to block the effect of a naturally produced VMP-like protein.
Also included as part of the present invention therefore are novel compositions comprising nucleic acids which encode a VMP-like protein. It will, of course, be understood that one or more than one gene may be used in the methods and compositions of the invention. The nucleic acid delivery methods may thus entail the administration of one, two, three, or more, homologous VMP-encoding genes. The maximum number of genes that may be applied is limited only by practical considerations, such as the effort involved in simultaneously preparing a large number of gene constructs or even the possibility of eliciting an adverse cytotoxic effect.
The particular combination of genes may be two or more distinct genes; or it may be such that a vls gene is combined with another gene and/or another protein, cofactor or other biomolecule; a cytokine gene may even be combined with a gene encoding a cell surface receptor capable of interacting with the polypeptide product of the first gene.
In using multiple genes, they may be combined on a single genetic construct under control of one or more promoters, or they may be prepared as separate constructs of the same or different types. Thus, an almost endless combination of different genes and genetic constructs may be employed. Certain gene combinations may be designed to, or their use may otherwise result in, achieving synergistic effects in affording protection against Borrelia and or stimulation of an immune response. Any and all such combinations are intended to fall within the scope of the present invention. Indeed, many synergistic effects have been described in the scientific literature, so that one of ordinary skill in the art would readily be able to identify likely synergistic gene combinations, or even gene-protein combinations.
It will also be understood that, if desired, the nucleic acid segment or gene encoding a VMP-like protein could be administered in combination with further agents, such as, e.g., proteins or polypeptides or various pharmaceutically active agents. So long as the composition comprises a vls gene, there is virtually no limit to other components which may also be included, given that the additional agents do not cause a significant adverse effect upon contact with the target cells or host tissues. The nucleic acids may thus be delivered along with various other agents as required in the particular instance.
Kits
Therapeutic kits comprising VMP-like peptides or VMP-encoding nucleic acid segments comprise another aspect of the present invention. Such kits will generally contain, in suitable container means, a pharmaceutically acceptable formulation of a VMP-like peptide or a VMP-encoding nucleic acid composition. The kit may have a single container means that contains the VMP composition or it may have distinct container means for the VMP composition and other reagents which may be included within such kits.
The components of the kit may be provided as liquid solution(s), or as dried powder(s). When the components are provided in a liquid solution, the liquid solution is an aqueous solution, with a sterile aqueous solution being particularly preferred. When reagents or components are provided as a dry powder, the powder can be reconstituted by the addition of a suitable solvent. It is envisioned that the solvent may also be provided in another container means.
Kits may also comprise reagents for detecting VMP-like polypeptides, such as required for immunoassay. The immunodetection reagent will typically comprise a label associated with the antibody or antigen, or associated with a secondary binding ligand. Exemplary ligands might include a secondary antibody directed against the first antibody or antigen or a biotin or avidin (or streptavidin) ligand having an associated label. Of course, a number of exemplary labels are known in the art and all such labels may be employed in connection with the present invention. The kits may contain antibody-label conjugates either in fully conjugated form, in the form of intermediates, or as separate moieties to be conjugated by the user of the kit.
The container means will generally include at least one vial, test tube, flask, bottle, syringe or other container means, into which the antigen or antibody may be placed, and preferably suitably aliquoted. Where a second binding ligand is provided, the kit will also generally contain a second vial or other container into which this ligand or antibody may be placed. The kits of the present invention will also typically include a means for containing the antibody, antigen, and reagent containers in close confinement for commercial sale. Such containers may include injection or blow-molded plastic containers into which the desired vials are retained.
VMP Antibodies
In another aspect, the present invention contemplates an antibody that is immunoreactive with a polypeptide of the invention. An antibody can be a polyclonal or a monoclonal antibody. In a preferred embodiment, an antibody is a monoclonal antibody. Means for preparing and characterizing antibodies are well known in the art (See, e.g., Howell and Lane, 1988).
Briefly, a polyclonal antibody is prepared by immunizing an animal with an immunogen comprising a polypeptide of the present invention and collecting antisera from that immunized animal. A wide range of animal species can be used for the production of antisera. Typically an animal used for production of anti-antisera is a rabbit, a mouse, a rat, a hamster or a guinea pig. Because of the relatively large blood volume of rabbits, a rabbit is a preferred choice for production of polyclonal antibodies.
Antibodies, both polyclonal and monoclonal, specific for VMP-like polypeptides and particularly those represented by SEQ ID NO:2, variants and epitopes thereof, may be prepared using conventional immunization techniques, as will be generally known to those of skill in the art. A composition containing antigenic epitopes of VMP can be used to immunize one or more experimental animals, such as a rabbit or mouse, which will then proceed to produce specific antibodies against vls expression and silent regions. Polyclonal antisera may be obtained, after allowing time for antibody generation, simply by bleeding the animal and preparing serum samples from the whole blood.
To obtain monoclonal antibodies, one would also initially immunize an experimental animal, often preferably a mouse, with a VMP composition. One would then, after a period of time sufficient to allow antibody generation, obtain a population of spleen or lymph cells from the animal. The spleen or lymph cells can then be fused with cell lines, such as human or mouse myeloma strains, to produce antibody-secreting hybridomas. These hybridomas may be isolated to obtain individual clones which can then be screened for production of antibody to the desired VMP peptide.
Following immunization, spleen cells are removed and fused, using a standard fusion protocol with plasmacytoma cells to produce hybridomas secreting monoclonal antibodies against VMP. Hybridomas which produce monoclonal antibodies to the selected antigens are identified using standard techniques, such as ELISA and Western blot methods. Hybridoma clones can then be cultured in liquid media and the culture supernatants purified to provide the VMP-specific monoclonal antibodies.
It is proposed that the monoclonal antibodies of the present invention will find useful application in standard immunochemical procedures, such as ELISA and Western blot methods, as well as other procedures which may utilize antibody specific to VMP epitopes.
Additionally, it is proposed that monoclonal antibodies specific to the particular polypeptide may be utilized in other useful applications. For example, their use in immunoabsorbent protocols may be useful in purifying native or recombinant VMP species or variants thereof.
In general, both poly- and monoclonal antibodies against VMP may be used in a variety of embodiments. For example, they may be employed in antibody cloning protocols to obtain cDNAs or genes encoding VMP or related proteins. They may also be used in inhibition studies to analyze the effects of VP in cells or animals. Anti-VMP antibodies will also be useful in immunolocalization studies to analyze the distribution of VMP peptides during various cellular events, for example, to determine the cellular or tissue-specific distribution of the VP peptide under different physiological conditions. A particularly useful application of such antibodies is in purifying native or recombinant VMP, for example, using an antibody affinity column. The operation of all such immunological techniques will be known to those of skill in the art in light of the present disclosure.

VMP-like sequences of pathogenic borrelia

Board of Regents, The University of Texas System


This invention provides a storage-stable dosage form of a thyroxine active drug composition which exhibits an improved stability. The formulation contains a thyroxine active drug substance, an alditol, and a saccharide, and, optionally, additional pharmaceutically accepted excipients. Levothyroxine sodium is the preferred active drug substance, mannitol is the preferred alditol, and sucrose is the preferred saccharide. Additional preferred excipients include, for example, microcrystalline cellulose, crospovidone, magnesium stearate, colloidal silicon dioxide, and sodium lauryl sulfate.

1. Field of the Invention
The invention relates generally to the field of medicinal formulations, and more particularly to methods of preparing storage stable pharmaceutical compositions in unit dosage form of levothyroxine sodium with increased shelf life and compositions made by these methods.
2. Description of the Background Art
Thyroxine active drugs are known for both therapeutic and prophylactic treatment of thyroid disorders. For example, levothyroxine sodium is prescribed for thyroid hormone replacement therapy in cases of reduced or absent thyroid function in e.g., ailments such as myxedema, cretinism and obesity. See, for example, Post and Warren in Analytical Profiles of Drug Substances, Vol. 5, Florey (ed.); Academic Press, New York (1976), pp. 226-281. Levothyroxine sodium is quite unstable, hygroscopic and degrades rapidly when subjected to high humidity, light or high temperature. See, for example, Won, Pharm. Res. 9(1):131-137, 1992. Because of the chemicophysical properties of the drug, formulations of levothyroxine sodium have extremely short stability duration, worsened under conditions of high humidity and temperature. Tablets may decompose approximately 1 percent per month. Gupta et. al., J. Clin. Pharm. Ther. 15:331-335, 1990. The stability problem has been so widespread that some drug companies marketing levothyroxine sodium tablets have been forced to recall various batches due to lack of stability.
Formulations containing levothyroxine sodium have been known in the art since the late 1950s. There have been recent attempts to develop more stable dosage formulations of levothyroxine sodium. For example, U.S. Pat. No. 5,635,209 discloses levothyroxine sodium in combination with potassium iodide as part of a stabilizing excipient. In the manufacture of this formulation, levothyroxine sodium was first mixed with microcrystalline cellulose, and then added to a dried granulation of potassium iodide and microcrystalline cellulose. The formulation purportedly provided increased active drug potency over a three month period in comparison to then commercially available formulations.
U.S. Pat. No. 5,225,204 discloses a complex of levothyroxine sodium and a cellulose, polyvinylpyrrolidone or Poloxamer. The formulation may be prepared by dissolving the drug complex in a polar organic solvent, adding a cellulose carrier to the liquid, and drying the resulting mixture to obtain a complex of levothyroxine sodium and polyvinylpyrrolidone or Poloxamer adsorbed on the cellulose carrier.
Although purportedly increasing the stability of the formulation, the deposition onto cellulose may have resulted in some increased stability due to improved content uniformity. Tests of such combinations yielded stability results at best equal to commercially available preparations such as those described in U.S. Pat. No. 5,955,105, and in some cases substantially worse.
The inventors of this stabilized composition teach one of skill in the art away from the use of carbohydrates in levothyroxine sodium formulations, stating that instability of the dosage form was the result of an interaction between the active drug substance and carbohydrate excipients.
The inventors of U.S. Pat. No. 5,955,105 also teach that the instability of thyroxine drugs is due to an interaction between the drug and the excipient. These inventors incorporated into the formulation a soluble glucose polymer designed to eliminate the interaction between the drug and other excipients contained in the final blend.
Because of degradation of the active ingredient in currently available formulations of levothyroxine sodium, new methods of formulating solid dosage forms of this drug would be highly desirable. Although different methods for producing a formulation stable enough to meet requirements for shelf-life have been attempted, no method has been entirely successful. There is, then, a great need for new formulations of thyroxine active drugs with increased stability and shelf life.
The present invention relates to methods and compositions which increase the stability of levothyroxine sodium and other thyroxine active drugs. This invention prevents the decreases in effective dosage which plague prior art thyroxine active drug formulations and substantially increases shelf life. The compositions include an active thyroxine drug with an alditol and a saccharide. Other optional ingredients in the composition include but are not limited to pharmaceutically acceptable excipients such as cellulose polymers or carbohydrates, disintegrants, lubricants and glidants.
Accordingly, the present invention provides a storage stable oral pharmaceutical composition which comprises a therapeutically effective amount of a thyroxine active drug and stabilizing amounts of an alditol and a saccharide. In a preferred embodiment, the thyroxine active drug is levothyroxine sodium, the alditol is mannitol, and the saccharide is sucrose. In yet another embodiment, compositions of the invention comprise at least one further pharmaceutical excipient, such as a carbohydrate, a starch or a modified starch, for example microcrystalline cellulose. In yet a further embodiment, this invention provides storage stable oral pharmaceutical compositions in unit dosage form comprising the compositions discussed above, and particularly a storage stable oral dosage form composition which comprises levothyroxine sodium, mannitol, sucrose, and optionally further comprises microcrystalline cellulose, polyvinylpyrrolidone, crospovidone, magnesium stearate, sodium lauryl sulfate, and colloidal silicon dioxide. The invention preferably provides such storage stable oral dosage forms in the form of tablets.
A preferred embodiment of the invention encompasses a storage stable oral pharmaceutical composition which comprises a therapeutically effective amount of levothyroxine sodium; about 58% by weight mannitol; about 14% by weight sucrose; about 25% by weight microcrystalline cellulose; about 1.5% by weight polyvinylpyrrolidone; about 1.4% by weight magnesium stearate; about 0.3% by weight colloidal silicon dioxide; and about 0.1% by weight sodium lauryl sulfate.
Another preferred embodiment of the invention encompasses a storage stable oral pharmaceutical composition which comprises a therapeutically effective amount of levothyroxine sodium; about 39% by weight mannitol; about 23% by weight sucrose; about 28% by weight microcrystalline cellulose; about 1.5% by weight polyvinylpyrrolidone; about 6% by weight crospovidone; about 2% by weight magnesium stearate; about 0.3% by weight colloidal silicon dioxide; and about 0.1% by weight sodium lauryl sulfate.
The present invention relates to storage stable granulation intermediates and oral pharmaceutical compositions in unit dosage form of a thyroxine active drug and methods by which they are produced. The methods involve a granulation intermediate containing the thyroxine active drug substance, an alditol, and a monosaccharide or disaccharide to provide a formulation with an increase of stability of both the granulation intermediates and the final oral dosage forms prepared from these granulation intermediates. Thus, the present invention provides a stable dosage form in which the dosage of thyroxine active drug is maintained at a predictable level for a longer period of time.
Formulations of levothyroxine with greatly increased resistance to degradation can be produced by providing excipients which reduce or eliminate degradation of the active substance. Although the prior art indicates that reaction between levothyroxine sodium and certain carbohydrate, monosaccharide or disaccharide excipients is responsible for the poor stability of the drug, the present inventive formulation achieves surprisingly stable levothyroxine dosage forms using these previously disfavored excipients. Additionally, preferred formulations are maintained at a pH of less than about 10.
The methods and formulations of this invention take advantage of the discovery that including an alditol and a saccharide results in a surprisingly stable levothyroxine sodium composition. This invention can be used to produce stable formulations of any natural or synthetic thyroid hormone replacement drug. Therefore, although the following description and example refer to compositions and methods using levothyroxine sodium, the invention is understood to encompass other thyroid hormone medications of the general formula
wherein R1 and R3 may be the same or different and are selected from hydrogen; halogen; alkyl; aryl; cycloalkyl; heterocycloalkyl; amide; alcohol; acid; ester; ether; acyl; alkenyl; and alkynyl; wherein R2 is
wherein R4 and R5 may be the same or different and are selected from hydrogen; halogen; alkyl; aryl; cycloalkyl; heterocycloalkyl; amide; alcohol; acid; ester; ether; acyl; alkenyl; and alkynyl. The medication can be in the form of a free acid, a free base, an organic salt, an inorganic salt, or a hydrate. Liothyronine is an example of a drug encompassed by the above-mentioned general formula.
According to this invention, stabilized pharmaceutical compositions are produced by blending the active ingredient with an alditol and a saccharide such as a monosaccharide or disaccharide to form a granulation intermediate. Addition of any additional pharmaceutical excipients, diluents or granulation aids is optional. Generally, further pharmaceutical excipients are added to produce final oral dosage forms such as tablets or capsules.
Formulations according to this invention are made according to the following general steps. Those of skill in the art are aware of equivalent methods and variations which produce the same general result. Therefore, the general instructions and the example which follows should not be considered to be strictly limiting. The active thyroxine ingredient, for example, levothyroxine sodium, is blended with an alditol and/or a saccharide to form a pre-blend for ease of handling. Preferred granulation intermediates are produced by making a wet granulation of the active ingredient with an alditol such as mannitol, a saccharide such as sucrose and a granulation aid such as microcrystalline cellulose. Preferably, the active ingredient is blended first with the alditol, sucrose is then added and the material is blended again. According to the invention, further excipients such as microcrystalline cellulose (also polyvinylpyrrolidone as binder) may also be incorporated into the granulation, but need not be added until the active ingredient is intimately mixed with the alditol and/or the sucrose. Therefore, the microcrystalline cellulose or other diluent functions as a granulation aid and compression enhancer (for tablet or capsule formulations) and not as a specific carrier for the thyroxine active drug.
In preferred embodiments, the wet granulation is dried, milled and optionally further blended. The granulation intermediate then may be stored or directly mixed with further ingredients to form a composition suitable for compression into tablets, filling into capsules or dissolved or suspended to form a liquid dosage form.
Without wishing to be bound by theory, it is believed that the stabilizing effect achieved with the inventive formulations is due to the presence of the alditol and the saccharide in the final dosage form, and specifically the mixing of the alditol and saccharide with the active ingredient at an early stage of manufacture. Preferably, processing of the active ingredient should be conducted at temperatures below about 45xc2x0 C.
Alditols which are suitable for use in this invention are those whose presence stabilizes the thyroxine drug. Alditols are widely known in the art. Preferred Elf ralditols include, but are not limited to, one or more of the following: mannitol, sorbitol, maltitol and xylitol. Most preferably, the alditol is mannitol. Saccharides for use with this invention are those that stabilize the thyroxine drug. Such saccharides include one or more monosaccharides, disaccharides and oligosaccharides composed of 2-10 monosaccharides. Monosaccharides, also known as reducing sugars, which may be used in the present invention generally include aldoses, hemiacetals and cyclic hemiacetals. Disaccharides are generally defined as two monosaccharide units joined together by a glycoside linkage. Oligosaccharides are generally defined as carbohydrates that hydrolyze to yield 2 to 10 molecules of a monosaccharide. Preferred monosaccharides, disaccharides, and oligosaccharides include, but are not limited to: sucrose, maltose, cellobiose, lactose, trehalose, glucose, fructose, galactose, ribose or deoxyribose. Preferably, the saccharide is a monosaccharide or a disaccharide, and more preferably is a disaccharide. The most preferred saccharide is sucrose.
Pharmaceutical compositions of this invention may be prepared for administration orally, rectally, vaginally, transmucosally, transdermally, parenterally, subcutaneously, and intramuscularly. Pharmaceutically acceptable excipients which are suitable for use in formulations for these methods of administration are known to those of skill in the art and may be included in formulations according to this invention. Generally, excipients contemplated for use in the inventive formulations may include, but are not limited to adjuvants; preservatives; buffers; fillers, extenders, carriers, binders and diluents; glidants and lubricants; surfactants, wetting agents and surface active agents; suspending agents and solvents. Compounds such as dyes and colorants, sweeteners, flavorings, perfuming agents and taste-masking ingredients also may be included in formulations according to this invention. Any pharmaceutically acceptable excipient, such as ingredients to aid in processing or to improve taste or appearance are contemplated for use with these formulations. Further excipients may be included according to the judgment of the pharmaceutical scientist formulating the medicament. In addition, other active ingredients may be included to produce a dual or multiple ingredient medication.
Exemplary surfactants and surface active agents may be selected from known pharmaceutical excipients such as, for example, gelatin, casein, lecithin, gum acacia, stearic acid or other fatty acids, benzalkonium chloride, calcium stearate, glyceryl monostearate or other fatty acid salts, polyethylene glycols, silicon dioxide, methylcelluloses or carboxymethylcelluloses, sodium stearyl fumarate, magnesium stearate, alginate, or any other surface modifying compounds known in the art. Compounds which function as wetting agents, such as, for example, pharmaceutically acceptable detergents and cetyl alcohols also are contemplated for use with the inventive formulations.
Lubricants such as talc, calcium stearate, sodium stearyl fumarate, stearic acid, magnesium stearate, solid polyethylene glycols and cocoa butter are useful with the inventive formulations, as are one or more binders, fillers or extenders such as starches, lactose or other sugars, polyvinylpyrrolidone, sodium citrate, dicalcium phosphate and other alkaline inorganic salts, carboxylmethylcellulose and other cellulose polymers, alginates, gelatins, microcrystalline cellulose, sorbitol, sodium chloride, chitosan, hydrogenated vegetable oil, kaolin, glycerol palmitostearate, magnesium carbonate, and calcium carbonate.
Solid dosage forms which may be prepared according to this invention can include tablets, capsules, rectal or vaginal suppositories, pills, dragees, lozenges, granules, beads, microspheres, pellets and powders, or any combination thereof. Formulations also may be prepared in the form of solutions, suspensions, emulsions, syrups and elixirs. These liquid dosage forms may include liquid diluents in addition to the solid ingredients discussed above. Such diluents may include, but are not limited to solvents, solubilizing agents, suspending agents and emulsifiers such as water or saline solutions, ethanol and other pharmaceutically acceptable alcohols; ethyl carbonate; ethyl acetate; propylene glycol; dimethyl formamide; pharmaceutically acceptable oils such as cottonseed, corn, olive, castor and sesame; fatty acid esters of sorbitan; polyoxyethylene sorbitol; and agar-agar. Formulations can be either immediate or modified release.
The formulations of this invention may be used for any convenient dosage amount of the active ingredient. Generally, the level of the active ingredient may be increased or decreased according to the judgment of the physician, pharmacist, pharmaceutical scientist or other person of skill in the art. The amount of the remaining non-active ingredients can be adjusted as needed. Preferably, the amount of alditol is adjusted to compensate for changes in the amount of active ingredient.
The preferred active ingredient in the formulations of this invention is levothyroxine sodium. Therapeutically effective dosage amounts for this drug generally range from about 0.1 xcexcg to about 5000 xcexcg and are most preferably from about 25 xcexcg to about 300 xcexcg. Exemplary dosages therefore include, but are not limited to 20 xcexcg, 25 xcexcg, 50 xcexcg, 75 xcexcg, 88 xcexcg, 100 xcexcg, 112 xcexcg, 125 xcexcg, 150 xcexcg, 175 xcexcg, 200 xcexcg and 300 xcexcg. Preferred solid dosage forms prepared according to this invention contain the following compounds: levothyroxine sodium (active drug substance); mannitol; microcrystalline cellulose (diluent); polyvinylpyrrolidone (binder); sucrose; crospovidone (disintegrant); magnesium stearate (lubricant); sodium lauryl sulfate (surfactant); and colloidal silicon dioxide (glidant).
Formulations of thyroxine active drugs prepared according to this invention contain about 0.1 xcexcg to about 5000 xcexcg thyroxine active drug substance, preferably about 1 xcexcg to about 1000 xcexcg and most preferably about 25 xcexcg to about 300 xcexcg. Alditols should be present at from about 5% to about 90% (by weight) of the final formulation, preferably from about 15% to about 80% and most preferably from about 25% to about 70%. Filler, such as carbohydrates (starch or cellulose polymer), for example microcrystalline cellulose, generally should comprise from about 5% to about 90% by weight of the final formulations, preferably from about 15% to about 80% and most preferably from about 25% to about 70%. Final dosage forms generally contain from about 5% to about 70% saccharide, by weight, preferably from about 10% to about 60%, and most preferably from about 20% to about 40%. Further optional ingredients in the final dosage form may include a disintegrant, which if present, generally forms from about 2% to about 30% of the final formulation by weight, preferably from about 2% to about 15% and most preferably from about 3% to about 10%. Lubricants may be present in the final formulation at from about 0.1% to about 5% by weight, preferably from about 0.2% to about 3% and most preferably from about 0.5% to about 2.5%. Glidants may be present in final formulations according to this invention at from about 0.05% to about 2% by weight, preferably from about 0.075% to about 1% and most preferably from about 0.1% to about 0.5%. Surfactants may be present in final formulation according to this invention at from about 0.005% to about 1% by weight, preferably from about 0.01% to about 0.5% by weight, and most preferably from about 0.01% to about 0.2%. Binders may be present in final formulation according to this invention at from about 0.1% to about 10% by weight, preferably from about 0.5% to about 5% by weight, and most preferably from about 1% to about 3% by weight.
After the solid ingredients of the formulation are blended, the stabilized drug preparation preferably is compressed into tablets. Alternatively, the preparation may be used to fill capsules such as hard gelatin capsules or used to prepare any other convenient solid dosage form. Compositions according to the invention may be stored in the form of powders, granulates, intermediates, suspensions, or solutions prior to addition of additional desired pharmaceutical excipients for the production of final dosage forms such as tablets or solid-filled capsules, or final liquid dosage forms such as solutions, syrups, suspensions, emulsions and the like.
The following example further illustrates the invention and is not to be construed to limit the claims in any manner.

Storage stable thyroxine active drug formulations and methods for their production